1. Field of the Invention
The present invention relates to a forming method of a silicide film, i.e., a method for forming an excellent cobalt silicide film, and particularly, it relates to a formation of titanium nitride on a cobalt film.
2. Description of Related Art
A typical method for forming cobalt silicide will be described with reference to FIG. 1. First, a silicone substrate is subjected to element separation by the use of a conventional technique to form a shallow trench isolation (STI) area and an active area in which a diffusion layer 100 is formed (FIG. 1A).
Subsequently, a natural oxide film on the diffusion layer 100 is removed as a pretreatment for depositing a cobalt (Co) film 101. The oxide film remained at an interface between the diffusion layer 100 and the cobalt film 101 disturbs the silicification of the cobalt film 101. In a typical method for removing the natural oxide film, a treatment of ammonia peroxide mixture (APM) and buffered hydrofluoric acid (BHF) is done for 60 seconds (this is corresponding to etching conditions for a thermal oxidation film of 20 Å), and further, an isopropylalcohol (IPA) drying is done.
Next, following steps are performed successively using a multi-chamber-sputter equipment. It is preferable to perform the steps successively because an oxidation of the substrate surface can be prevented and the silicification of the cobalt film 101 grows excellently thereby. Moreover, the sputter equipment is preferably used for processing the sequential steps successively. First, the substrate for treatment is carried in, thereafter a degassing is done, then ion of ionized sputter-gas (commonly argon) is directly irradiated onto the substrate to remove the natural oxide film remained on the surface of the substrate by a sputter-cleaning. After that, the cobalt film 101 is deposited in 60 Å using a cobalt target, and a titanium nitride (TiN) film 102 is deposited in 200 Å using a nitrogen (N2) and a titanium target (FIG. 1B). The titanium nitride film is common as a cap for the cobalt film during annealing.
Herein, for the conditions of respective treatments, the degassing is done at 300° C. for 60 seconds, the sputter-cleaning is done under the conditions that RF (60 MHz) is 360 W, HF (400 kHz) is 90 W, an argon flow rate is 40 sccm, and a process time is 13 seconds (this is corresponding to the etching conditions of the thermal oxide film of 40 Å). The sputter of cobalt is done by a collimation sputter under DC power of 1 kW, temperature of 200° C., respective argon flow rates of 15 sccm and 4 sccm in a chamber and a holder, and the process time of 28 seconds, and the sputter of titanium nitride is done under DC power of 2.5 kW, no heating, respective argon flow rates of 38 sccm and 4 sccm in the chamber and the holder, the nitrogen flow rate of 43 sccm, and the process time of 32 seconds.
At that time, the titanium nitride film is formed by a reactive sputter, where the titanium ejected from the titanium target is reacted with the nitrogen flowed into the chamber, resultantly titanium nitride is deposited on the substrate. While titanium nitride cannot be formed essentially unless titanium is heated at 800° C. or more in nitrogen atmosphere, the deposition is done under a non-thermal equilibrium state without heating, therefore titanium nitride contains certain titanium which is not reacted with nitrogen. When a cobalt monosilicide is formed by a first annealing in a later step, this titanium in titanium nitride plays an important role.
Typically, the natural oxide film is remained slightly on the diffusion layer even though the pretreatment and the sputter-cleaning are performed. It is considered that after titanium diffuses through cobalt and comes into the interface with the silicon wafer during the first annealing, titanium reduces the slightly remained natural oxide film and generates a silicide formable state for cobalt because it functions to reduce the oxide film. However, a single titanium film is not preferable for the cap film. It is because the single titanium also forms an alloy of cobalt and titanium, leading to difficulty for control of a thickness of cobalt silicide.
In this way, an RTA (Rapid Thermal Anneal) treatment as the first annealing is performed at 550° C. for 30 seconds under the nitrogen of 10 dm3/min so as to change the cobalt film 101 on the diffusion layer 100 in the active area to the cobalt monosilicide (CoSi) film 103 (FIG. 1C).
Then, the unreacted cobalt film 101 and the titanium nitride film 102 on the STI is removed by a batch type spray cleaning equipment, and the cobalt monosilicide film 103 is left only on the diffusion layer 100 (FIG. 1D). Finally, the RTA treatment as the second annealing is performed at 850° C. for 30 seconds under the nitrogen of 10 dm3/min so as to change the cobalt monosilicide film 103 on the diffusion layer 100 to the cobalt disilicide (CoSi2) film, consequently the formation of cobalt silicide is completed (not shown).
Now, in the above method, cobalt silicide is not formed excellently at the active area edges, as shown in the defect portion 104 in FIG. 1D. This is because the titanium target is nitrided due to the nitrogen flowed into the chamber of the sputter equipment when the titanium nitride film is formed by the reactive sputter, and excessive nitrogen atoms are supplied to the interface between the underlaid cobalt film and the titanium nitride film when the sputter of titanium nitride is performed onto the subsequently carried-in substrate. If the excessive nitrogen atoms exist, titanium in the titanium nitride film lowers its reduction function, the natural oxide film on the active area is hardly to be reduced, and the silicification of cobalt is restrained. It is considered that the reason why the defects occur at the active area edges is because the natural oxide film is apt to remain there.
The invention has been developed in consideration of the above problems that exists in conventional manufacturing methods of semiconductor devices, particularly the formation method of cobalt silicide. The invention intends to provide a novel and improved manufacturing method of the semiconductor device, which prevents the lowering of the reduction function of titanium in the titanium nitride film due to the excessive nitrogen atoms, allows the natural oxide film on the active area to be reduced and enhanced the silicification of cobalt, and enables the excellent cobalt silicide to be formed.